Simple low cost access to mobile phones has huge economic and social impacts; research from GSM Association has showed that an increase of just 10% of mobile penetration in a developing country will raise the economic growth rate by 1.2%. Industrial companies have been striving to develop low cost mobile handsets below $30 per unit, however the cost is still beyond much of the world's 6.3 bn population. According to a recent Nokia Study more than 50% of respondents in India and Pakistan and nearly 30% of respondents in Vietnam said they share, or would share, their mobile phone with family or friends. More and more families in the emerging markets are also purchasing mobile phones for pooled or shared usage with a family unit, or amongst a group of friends. However the shortcomings in the use of shared phones are that the individual subscriber does not have his own individual number to enable him to receive calls, or voice messages; that he has to carry on paper his own contact database and that all his call records remain on the shared phone he has used.
The use of USSD in GSM mobile networks is defined in 3GPP/ETSI GSM 02.90 (USSD Stage 1) and GSM 03.90 (USSD Stage 2) specifications. USSD works on all existing GSM MAP2+ handsets which is almost all existing handsets, with no handset or SIM card upgrade necessary. The potential of the pre-installed user base for USSD applications is therefore immense. It is a session orientated service, unlike SMS which is store and forward, which allows very fast communication between a handset and an application. Users do not need to access any particular handset menu to access services with USSD, they enter a defined USSD string from the handset, such as *#101#, to access a particular operator predefined service. USSD codes are routed back to the home mobile's network HLR and then onto the MSC and ultimately to the USSD gateway. The gateway will respond to the code in a predefined way.
The use of USSD to access information services, or to enable roaming on a prepaid account, or to manage prepaid accounts by doing a balance enquiry or credit recharge from a voucher is well detailed in industry related literature and know-how. For example, U.S. patent application Ser. No. 11/225,636 by Zabawskyj, et al. Entitled Method and system for international roaming and call bridging and U.S. Pat. No. 6,975,852 by Sofer, et al. Entitled System and method for roaming for prepaid mobile telephone service. However the use of USSD to enable personalised shared mobile phone usage is innovative.